Calendar roll system

ABSTRACT

A high-precision, metal-faced, calendar roll which can be readily reconditioned by thermal means. The calendar roll has a surface which is advantageously formed of that class of nickel-titanium alloys having thermally-responsive shape memory properties. The calendar roll is particularly useful in avoiding time consuming repair and undesirably prolonged runs in making high quality magnetic tape.

BACKGROUND OF THE INVENTION

The invention relates to forming a novel calender roll apparatus of thetype used in web-processing to assure an excellent finish to the webbeing subjected to the calendering action.

Although calendering of some webs, e.g. paper, may be relativelynon-critical operations, there are many problems involved in criticalcalendering operations, e.g. those in which high-quality magnetic tapeis calendered.

In such calendering, the magnetic tape web is pressed between two rolls.The rolls are being pressed together by forces of the order of 50,000pounds. The coating is densified and smoothed by this process. There aretwo general categories:

(i) The two rolls are the same material, e.g. steel against steel;

(ii) The two rolls are of different material, e.g. steel against cotton,plastic, rubber, paper, etc.

In the first situation, the problem is that the steel rolls must be verycarefully made, to be sure that they give uniform pressure against thetape surface. Some manufacturers will keep their spare rolls turning 24hours a day to avoid sag caused by gravity deforming the rolls. Suchdeforming can cause alternately smooth and rough surfaces as the roll isrotated against the sheet being calendered. Also, any crease orirregularity in the web can so damage a steel roll, that it must beturned down, chrome plated again, and polished. The advantages of steelrolls on calenders is their ability to withstand high pressures in thenip and better heat transfer.

In the second situation, the compliant roll solves many of themechanical problems of alignment and careful tolerances. Other problemsare presented by compliant-surfaced rolls. Such rolls, typically ofpaper and cotton, are not very strong, so nip pressures must be low.They break down and have to be reground and replaced. A crease in theweb will mar the surface of the roll and it will have to be reground.Plastic-faced rolls have been tried and they are successfully used.However, advantageous use of plastic is limited to lower operatingtemperatures. As the calender turns, the deformation of the compliantroll manifests itself in generating of heat. Plastic and cotton are poormaterials for use in removing such heat; they have low thermalconductivity. The result is that the heat builds up at the edges of theroll and the roll gets even softer at such cites, causing moredeformation and still more heat build-up along the edges. The edge ofthe web may reach 40° F. or 50° F. above the middle of the roll.Non-uniform expansion of the roll and non-uniform webs result.

Soft metal surfaces have been tried for complaint rolls. This causeslots of problems because the surfaces are usually not corrosionresistant under plant operating conditions. Again, a crease in the webbeing processed "wipes out" the roll and necessitates regrinding andrefinishing. In general, it may be said that critical calenderoperations in the prior art relating to magnetic tape use two to fivenips with one relatively compliant roll at each nip.

Another aspect of earlier art, one heretofore unrelated to calenderdesign, is the existence of certain titanium/nickel alloys. Thesematerials have been called NITINOL materials because of their nickel andtitanium content and the fact that they were developed at the NavelOrdinance Laboratories. The material has been very expensive, on theorder of 100 to 1,000 times as expensive as metals. Its use has beenheretofore restricted to such applications as small, highly-criticalconnections for electrical applications such as those required by theU.S. Navy to operate at 6,000 psi or 3,000 psi in temperature of 65° F.to 575° F. Another application which may have become commercial is theuse of such materials in formation of dental braces. Various suchmaterials, or related materials, are disclosed in, or discussed in, U.S.Pat. Nos. 3,352,650; 3,174,851; 3,558,369; and 3,660,082.

Still another aspect of earlier art, an aspect not heretofore related tothe aforesaid alloy art, is the manufacture of magnetic tape. Of course,it was well known that one should calender tape and that one had torefurbish calender rolls occasionally. However, the value ofconsistently good calender performance was not believed to have beenfully appreciated. Yet, it is an important aspect of this invention thatsuch performance is recognized to be very valuable and to justify therelatively high cost of the aforesaid NITINOL materials in calenderapplications.

It is emphasized that this section on the prior art is prepared inhindsight with full knowledge of the invention disclosed below. Thus, nopre-existing relationship of disparate elements of the prior art is tobe construed from this section.

SUMMARY OF THE INVENTION

Therefore, it is a principal object of the invention to provide animproved calender, one which is readily and inexpensively refurbished.

Another object of the invention is to provide a calender systemcomprising two such rolls.

A further object of the invention is to provide a means for facilitatingthe economic manufacture of consistently superior magnetic tape and toprovide an improved process for making such tape without the need ofremoving a calender roll from the like during the manufacturing process.

Other objects of the invention will be obvious to those skilled in theart on their reading of this disclosure.

The above objects are achieved by the formation and utilization of acalender roll comprising as the surface thereof a thin layer of a metalalloy, advantageously a NITINOL alloy, which has a "shape-memory"because it actually "remembers" its original shape after beingplastically deformed and returns to this shape when later heated above atransformation temperature.

The NITINOL material having "shape-memory" characteristics has a numberof advantages:

1. If creased, the material has memory and will come back to itsoriginal shape on heating of the calender roll.

2. The basic mechanical and thermal properties of these alloys fit theapplication in an extraordinary way. They are softer than the steel rollbut much harder than the other compliant roll choices and they arenon-magnetic. They have good thermal conductivity far better than thethermal conductivity of plastic, paper or felt rolls.

3. The NITINOL alloy has extraordinary resistance to corrosive attack.The copper oxide, or lead oxide, associated with other soft metals willnot occur. The material does not crack as the result of stresscorrosion.

These properties are particularly important during the processing ofmagnetic tape, e.g. a web consisting of a polyester substrate carrying aresin coating in which is dispersed magnetic particles. For example, theNITINOL alloys useful in the invention, or any equivalent alloy, aresufficiently harder than the tape being processed to represent a majoradvantage over other complaint rolls. Thus, not only is it possible toachieve a relatively quick repair of the roll, it is possible to avoidthe need for such repair for a longer period of time.

These factors translate into making it economically feasible to producea more dependably calendered (and therefore more dependably compactedand defect free) magnetic tape. This means improved short waveperformance of the tape at high frequencies--this believed to resultfrom an increase in density of the recording medium on the tape and,also, the ability to have the recording head closer to the tape which,because of the better compaction, has fewer and less severe asperities.Indeed, the major advance achieved by use of the invention is believedto be the ability to consistently and economically manufacture amagnetic tape with an improvement in magnetic signal processingcharacteristics rather than the more dramatic advantage of contributingto relatively simple maintenance procedures by utilizing a"shape-remembering" metal.

It is one advantage of the invention that, for the first time, it ispossible to use two compliant rolls, e.g. two NITINOL rolls to form acalender nip. Moreover, whereas it has heretofore been the practice touse three or four nips to calender a magnetic tape web, it is nowpossible to achieve such calendering with two nips or even one nip.

ILLUSTRATIVE EMBODIMENT OF THE INVENTION

In this application and accompanying drawings there is shown anddescribed a preferred embodiment of the invention and suggested variousalternatives and modifications thereof, but it is to be understood thatthese are not intended to be exhaustive and that other changes andmodifications can be made within the scope of the invention. Thesesuggestions herein are selected and included for purposes ofillustration in order that others skilled in the art will more fullyunderstand the invention and the principles thereof and will be able tomodify it and embody it in a variety of forms, each as may be bestsuited in the condition of a particular case.

In The Drawings

FIG. 1 is a perspective, somewhat schematic and partially in section, ofa calender roll constructed according to the invention.

FIGS. 2 and 3 are schematic diagrams of a calendering system accordingto the invention.

Referring to FIG. 1, it is seen that as otherwise conventional, cooledcalender roll 10 is formed of an exterior sleeve 12 of 3/16-inchthickness of a NITINOL alloy obtained from Raychem Corporation andcharacterized by an ability to heal plastic imperfections, such as minorindentations at a temperature below 120° C. The sleeve is supported on acylindrical support shell member 14 which is contained by circular heads16 fastened into member 14 by bolts 18. A concentric pipe system 20comprises a fluid inlet pipe 22 and a fluid outlet conduit 24, theconduit being formed by the exterior of pipe 22 and the interior ofjournal member 26. This system 20 allows heating or cooling fluid to becirculated through reservoir 23 and thence to an annular passage 30between perforated tube 32 and shell member 14.

A small ball bearing, e.g. a bearing of about 3/16-inch diameter washammered against sleeve 12 to cause a dimple therein. Thereupon, thesleeve can be heated to 125° C. whereupon the dimple wholly disappears.

FIG. 2 illustrates a system wherein magnetic tape 40 from a coating lineenters an oven 42 and is then calendered between a steel roll 44 and ahot-oil heated compliant roll 46 comprising a NITINOL sleeve, thencethrough a slitter mechanism 48 and into spools 50. For the first time,it is possible to use a metallic compliant roll and to heal anyimperfections therein by simple heat-treatment of the roll in-place,e.g. by use of radiant heaters such as ultra-violet lights 52.

It will be understood that the number of nips and rolls in the calendercan be increased to, e.g. five rolls and four nips. However, it isbelieved that two, or even one, nip is made of a NITINOL-type,memory-type, metal.

In one advantageous embodiment of the invention, a "space calender" isincorporated into the web processing equipment and when one calenderneeds refurbishing, the web is transferred through a second calender.Thus, as seen in FIG. 3, a first calender comprising NITINOL rolls 46,is being refurbished by radiant heaters 66, an alternate calender systemcan be brought into use by closing the nip between NITINOL rolls 76.

It is also to be understood that the following claims are intended tocover all of the generic and specific features of the invention hereindescribed and all statements of the scope of the invention which mightbe said to fall therebetween.

What is claimed is:
 1. A calender roll system, having (A) as a compliantroll thereof, a calender roll comprising, as a surface thereover, asleeve of a shape-memory alloy which is plastically deformablecharacterized by an ability after its surface is marred, to return toits original shape after being heated at a transformation temperature;and (B) a second roll forming means adjacent said compliant roll toforce a web against said compliant roll.
 2. A calender system as definedin claim 1 wherein said compliant roll is formed of a NITINOL alloy. 3.A calender system as defined in claim 2 wherein said transformationtemperature is 125° C. or less.
 4. A calender system as defined in claim3 wherein said calender roll is formed of a NITINOL alloy.
 5. A calendersystem as defined in claim 3 wherein said second roll is also formed ofa shape-memory alloy characterized by an ability to return to itsoriginal shape after being heated at a transformation temperature.
 6. Acalender system as defined in claim 1 wherein said second roll is alsoformed of a shape-memory alloy characterized by an ability to return toits original shape after being heated at a transformation temperature.